ABSTRACT
Both the (dγt/dt)max and Llamellae of the 1.0 mM aqueous C12En solutions as a function of EO units are shown in Fig. 10 [78]. A linear increase in (dγt/ t)max was observed in the region of EO units less than 40. When EO units exceed 40, (dγt/dt)max seems unchanged. On the other hand, the steep decrease in Llamellae was observed in the region of EO units less than 10. Particularly, when EO units reach 40, the lamella is difficult to elongate (Llamellae is only 1.7 mm). Compared with the experimental results for the Ross-Miles foam behavior as shown in Fig. 9, (dγt/dt)max seems to correlate to the initial foam height, while Llamellae seems to correlate to the residual foam height after 5
min. This coincidence indicates that the solutions having a large (dγt/dt)max value have a potential for making a large total surface area of bubbles, because (dγt/dt)max reflects the maximum rate of the decrease in the surface tension under a constant value in the work of foam generation. Therefore the initial foam height for the Ross-Miles technique is in good concordance with the value of (dγt/dt)max. On the other hand, the residual foam height ratio for this method is in good concordance with Llamellae, because Llamellae reflects the durability of lamella under elongation. We believe that the increase in EO units on
initial foam height has a tendency to generate bubbles easily. In fact, the initial foam height of surfactants having EO units within 5 to 15 increases from 60 to 140 mm. These increases correlate to the increase in the values of (dγt/dt)max from 28 to 278 mN m−1 sec−1. Despite the increase in the value of (dγt/dt)max from 519 to 770 mN m−1 sec−1, the decrease in initial foam height is observed when EO units are from 22 to 53. This indicates that excessive decrease in surface tension generated by surfactants having longer EO units would weaken a restoring force in resisting the thinning of the lamella. On the contrary, the higher initial foam film stability, in the shorter EO region, would be caused by the Marangoni effect.
